One-component room temperature vulcanizable (RTV) silicone rubber compositions are well known in the art. Examples of such compositions are described in U.S. Pat. Nos. 3,035,016, 3,133,891 and 3,296,161. Such one-component room temperature vulcanizable silicone rubber compositions generally consist of a silanol endstopped linear diorganopolysiloxane polymer, a filler, an organotriacyloxysilane as a cross-linking agent and a metal salt of a carboxylic acid as a catalyst. The one-component compositions cure to a solid, elastic state at room temperature upon exposure to moisture commonly present in the atmosphere.
One-component room temperature vulcanizable silicone rubbers of these types are extremely useful and are particularly adapted for caulking and sealing applications where strong adhesion to various surfaces is important. In the preparation of the one-component room temperature vulcanizable silicone rubber compositions, it has been observed that in certain instances, the addition of the cross-linking agent to the silanol endstopped linear diorganopolysiloxane results in a compound which has an abnormally high flow rate and which losses its thixotropic characteristics. The high flow rate increases the difficulty of applying the silicone rubber compositions to various surface areas, especially vertical surfaces, with any accuracy. The silicone rubber compositions possessing a high flow rate, have a tendency to spread from and flow out of the particular area to which they are applied resulting in a decrease in the effectiveness of such compositions for their intended purpose.
One method of lowering the flow rate of one-component room temperature vulcanizable silicone rubber compositions has involved the addition of a treated fumed silica filler alone, or in conjunction with a phenyl-containing polysiloxane fluid with high trifunctionality as disclosed in U.S. Pat. No. 4,000,129. In U.S. Pat. No. 4,000,129 at least 11 to 14 parts of such additives are incorporated into one-component room temperature vulcanizing systems per 100 parts of the base silanol endstopped diorganopolysiloxane polymer. While such additives are effective, the presence of the fumed silica, whether treated or untreated has a tendency to increase the modulus of elasticity of the cured silicone rubber formed from the composition. However, it is highly desirable to have room temperature vulcanizable silicone rubber compositions with as low a modulus of elasticity as possible, especially when such compounds are used as sealants. The lower the modulus of elasticity of the uncured rubber, the higher the elasticity of the rubber in the cured state. The elasticity of a cured rubber is a measure of such rubber's ability to absorb structural strain due to the movement of distinct surfaces which have been sealed with such rubber. Accordingly, it is desirable to provide a compound which will improve the flow properties of uncured room temperature vulcanizable silicone rubber compositions without a concurrent increase in the modulus of elasticity of such compounds.
Organopolysiloxane copolymers as disclosed in U.S. Pat. No. 3,629,165 consisting of a polysiloxane chain and a polyether chain which are linked together through various carboxyl alkyl radicals have been used as polyurethane foam additives. Such copolymers have made it possible to produce satisfactory polyurethane foams by a single step process instead of the customary two-step process. They act to give control of pore size and to guide toward closed- or open-cell types of foam. They make bubble formation easier, promote uniform cell size and prevent bubble coalescence. However, such compositions have not been heretofore used for improving the flow characteristics of one-component room temperature vulcanizable silicone rubber compositions or for improving the modulus of elasticity of one-component room temperature vulcanizable silicone rubber compositions.